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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From March 06, 2000 to March 21, 2000
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Preparation of the buffer solutions:
The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.

Preparation of the samples:
Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.5 g/L in the three buffer solutions.
In an attempt to minimise oxidation, individual aliquots, sealed in vessels containing an inert nitrogen gas headspace, were incubated at the test temperature for each time point to eliminate the need to expose the test solution to air when sampled. The solutions were shielded from light whilst maintained at the test temperature.
Details on test conditions:
Preliminary Test/Test 1
Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 120 hours.

Analysis of sample solutions:

Aliquots of the sample solutions were taken from the flasks at various times and the pH of each solution recorded. The concentration of the sample solution was determined by high performance liquid chromatography (HPLC).

Samples
Duplicate aliquots (A and B) of sample solution were diluted by a factor of five using reverse osmosis water for pH 7 and pH 9 samples and using pH 9 buffer for pH 4 samples. All diluting solvents were degassed with nitrogen prior to use.

Standards
Duplicate standard solutions of the test substance 70 % were prepared in the required sample matrix at a nominal concentration of 100 mg/L. A single marker standard of DADTL was prepared in reverse osmosis water at a nominal concentration of 200 mg/L for the 120 hour analysis only.
Transformation products:
yes
No.:
#1
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Key result
pH:
7
Temp.:
25 °C
Remarks on result:
other: The test substance 70 % could not be prevented from oxidising
Key result
pH:
9
Temp.:
25 °C
Remarks on result:
other: The test substance 70 % could not be prevented from oxidising

The test substance concentrations at the given time points:

pH 4 at 50.0 ± 0.5 °C

Time (h)

0

2.4

24

120

Conc. (g/L)

0.490

0.479

0.471

0.419

% of initial

100

97.8

96.2

85.4

 

There has been some loss of test substance due to oxidation. Therefore, an estimation has been done of approximately 10 % hydrolysis after 5 days at 50 °C, equivalent to a hydrolytic half-life greater than 1 year at 25 °C.

pH 7 at 50.0 ± 0.5 °C

Time (h)

0

2.4

24

120

Conc. (g/L)

0.571

0.479

0.444

0.231

% of initial

100

96.3

85.9

44.6

 

No estimation of hydrolytic half-life can be obtained due to oxidation of the test substance.

pH 9 at 50.0 ± 0.5 °C

Time (h)

0

2.4

24

120

Conc. (g/L)

0.515

0.490

0.355

0.156

% of initial

100

95.2

69.0

30.2

 

No estimation of hydrolytic half-life can be obtained due to oxidation of the test substance.

Validity criteria fulfilled:
yes
Conclusions:
Under the study conditions, the estimated hydrolytic half-life of the test substance at pH 4 (25 °C) was determined to be >1 year. Estimation of half-life at pH 7 and 9 could not be made because the test substance could not be prevented from oxidizing.

Executive summary:

A study was conducted to determine the hydrolytic stability of the test substance (Ammonium 2-mercaptopropionate) solution according to OECD Guideline 111. Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.5 g/L in the three buffer solutions pH 4, 7 and 9 and were maintained at 50.0 ± 0.5 °C for a period of 120 hours. To minimise oxidation, individual aliquots were sealed in vessels containing an inert nitrogen gas headspace. Aliquots of the sample solutions were taken from the flasks at various times and the pH of each solution recorded. The concentration of the sample solution was determined by high performance liquid chromatography (HPLC). Under the study conditions, the estimated hydrolytic half-life of the test substance at pH 4 (25 °C) was determined to be >1 year. Estimation of half-life at pH 7 and 9 could not be made because the test substance could not be prevented from oxidizing (O'Connor, 2000).

Description of key information

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
25 °C

Additional information

A study was conducted to determine the hydrolytic stability of the test substance (Ammonium 2-mercaptopropionate) solution according to OECD Guideline 111. Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.5 g/L in the three buffer solutions pH 4, 7 and 9 and were maintained at 50.0 ± 0.5 °C for a period of 120 hours. To minimise oxidation, individual aliquots were sealed in vessels containing an inert nitrogen gas headspace. Aliquots of the sample solutions were taken from the flasks at various times and the pH of each solution recorded. The concentration of the sample solution was determined by high performance liquid chromatography (HPLC). Under the study conditions, the estimated hydrolytic half-life of the test substance at pH 4 (25 °C) was determined to be >1 year. Estimation of half-life at pH 7 and 9 could not be made because the test substance could not be prevented from oxidizing (O'Connor, 2000).